Impact of autohydrolysis on wood components and on pure cellulose production

Hélène Curmi defended her doctoral thesis of the University Grenoble Alpes - prepared under the supervision of the Professor Christine Chirat and the Professor Emeritus Dominique Lachenal (Grenoble INP-Pagora/LGP2). She presented the results of her research work entitled Study of the impact of autohydrolysis on wood components and on delignification processes to produce pure cellulose.

This study is a part of a large project which aim is to convert a pulp mill into a fully integrated biorefinery by adding an autohydrolysis step to remove and valorize hemicelluloses prior to cooking.

This thesis’s goal is to study the impact of adding an autohydrolysis step on wood components and on the subsequent delignification and bleaching processes applied to this wood to produce pure cellulose. Wood components were analyzed before and after autohydrolysis. In particular it was shown that autohydrolysis increases the amount of free phenolic groups, and lowers the involvement of lignin in lignin carbohydrates complexes. A new NMR method using Dynamic Nuclear Polarization was performed directly on milled wood to look at wood components structure without extraction’s steps to avoid chemical modifications.

The second part describes the test of pulp processes (alkaline cooking, oxygen delignification and bleaching) on autohydrolysed wood chips. It showed that the addition of this autohydrolysis step improves delignification during cooking to such an extent that soda cooking alone is possible and efficient. Oxygen delignification was also improved. Two bleaching sequences with or without chlorinated compounds (ECF and TCF) were applied and compared, and it was concluded that sustainable bleaching without any chlorinated reagents is feasible. Finally, evaluation of bleached pulp properties demonstrated that viscose application can be targeted. Indeed, pulp had high purity cellulose content, adequate polymerization degree and high brightness and brightness stability.